1. Field of the Invention
The present invention relates to a key for intermittent electrical contact-connection of at least two conductors arranged on a printed circuit board to an electrically conductive contact element, in particular for fixing on the printed circuit board in the context of SMT technology. In this case, the key has at least one base arranged on the printed circuit board and also a key head—which is movable relative to the printed circuit board and the base—with the contact element, wherein the key head is connected to the base by means of at least one movable membrane, and wherein base and membrane are composed of an insulating elastic material. The present invention furthermore relates to methods for producing such a key or arrangements of such keys and uses of such keys.
2. Description of Related Art
Contact key switches are used for example for mobile telephones, remote controls and also for applications for example in vehicles, etc. They are normally based on keys or arrangements of keys which are composed of a rubber-like elastic material (normally silicone) and which are arranged on a printed circuit board, and wherein a contact element (for example a contact pellet composed of metal or carbon) is arranged on the underside of an actual key head, such that when this key head is depressed, the contact element is pressed onto the printed circuit board in such a way that conductors arranged thereon are connected to one another. Constructions of this type are disclosed in EP 0938111 for example.
Nowadays there are two fundamental solution approaches for realizing such a keypad with an overlying plastic cap.
The first solution involves silicone switching mats having at least one switching dome, but in general usually a plurality of switching domes on a mat. The switching domes are actuated by means of the plastic cap and yield a clearly defined force-displacement characteristic curve (tactile feedback). When the electrically conductive contact pellet touches the printed circuit board, the contact is closed and the switch is thus actuated. Switching mats are usually placed onto the printed circuit board manually. Backlighting of the plastic caps is effected by means of LEDs (light emitting diode) applied on the printed circuit board.
The second solution involves so-called tact switches. Tact switches are individual switching domes which are provided with one or more little feet which are soldered on the printed circuit board. Mounting is usually effected automatically by the SMT method (surface mount technology). The tact switches available nowadays are of complex construction and therefore very expensive. Backlighting of the plastic caps is usually effected by means of LEDs applied on the printed circuit board, but more recent variants also already have backlighting integrated in the tact switch. Only a few force-displacement variants are usually available.